In his 40 years of teaching, Al Hasvitz has always understood the importance of video aids in the classroom. “I am one of the few teachers in the United States who can thread a 16mm projector,” the award-winning social studies teacher from Walnut, Calif., boasts. But today, like most teachers, Hasvitz looks online to find instructional videos for his seventh grade students. In fact, he bookmarks more than 80 video websites. But how does he find quality content among all these options?

Online video has become a valuable 21st century learning tool, in and out of the classroom. In the last year, views of educational videos on YouTube doubled. But teachers still struggle to find safe and easy ways to find quality content for students. YouTube is the most common online source, accounting for 84 percent of the 181 million unique online video views in January 2012. But many school districts prohibit student access to YouTube, fearing distracting and inappropriate content. Some districts block the site entirely, others provide faculty passcodes, and a few require teachers to submit each video for approval.

“It takes away the spontaneity,” says Deven Black, a teacher-librarian in the Bronx, where the New York City Department of Education blocks YouTube completely. “If a topic comes up I can’t just search for it and use the video immediately. I have to download it at home in advance and transfer it to a different format. It just becomes more complex.”

But accessing video is becoming less cumbersome as innovators find new ways to aggregate and share quality educational clips. Hasvitz, for instance, primarily uses WatchKnowLearn, a free portal for teacher-approved videos. Other sites like SchoolTube and TeacherTube allow teachers and students to upload their own videos to share. And YouTube is actively seeking to join the curriculum. In December the site introduced a new network setting, YouTube for Schools, which allows access only to approved channels. When the school or district administrator enables the setting, teachers and students only have access to videos on the YouTube EDU section of the site, with comments and related videos hidden. An administrator can also enable access to additional channels, including those individual teachers create for classrooms. Hundreds of schools across the country have signed up since the December launch, says Angela Lin, head of YouTube EDU.

YouTube EDU currently features more than half a million videos on 750 channels from education partners, and although it was initially university focused, the site has recently been working to increase K-12 content. More channels are expected in the coming months, including some from big names like Amy Poehler, Rainn Wilson, and Participant Media, the film production company behind Food, Inc. and Waiting for “Superman.”

One of YouTube EDU’s most popular new channels has been TED-Ed, which launched its first 12 videos last month and had over one million views within one week. TED-Ed pairs teachers with animators to create short, engaging educational videos. Teachers are invited to submit their best lessons, and TED-Ed works with them to refine and record the script. Unlike other content from TED, each video, covering topics from ocean mysteries to the American election schedule, is only three to eight minutes long, perfect for initiating classroom discussion.

“We work really hard to ensure that we’re doing our best to celebrate these teachers’ voices,” says Logan Smalley, who heads TED-Ed. He highlights the “slightly unexpected but particularly fruitful partnership” between educators and animators. The YouTube channel is just the first step in TED-Ed’s mission to create and aggregate quality K-12 educational content—the next phase of the initiative launches later in April.

Still, YouTube for Schools may not yet be the perfect video source. Some firewalls block the site, and a number of teachers think the K-12 content is inadequate and hard to navigate. WatchKnowLearn remains a popular substitute, especially because the free site features most of YouTube’s educational content. Entirely funded by an anonymous donor, WatchKnowLearn functions as a wiki and has been building its library since 2008. It was created for teachers, by teachers.

“For four years teachers have gone out and loaded the videos and designed the directories,” says CEO Joe Thomas. “WatchKnowLearn is teacher designed, teacher rated, and teacher managed.”

YouTube retains incomparable content, if you know how to navigate it. Somewhere amid LOLcats and pirated SNL clips are thousands of videos explaining everything from equilateral triangles to the Roman Empire. “These other sites are all poor substitutes for YouTube in the classroom,” says Jason Mammano, an instructional technology facilitator of a large district in North Carolina. He regularly uses WatchKnowLearn, but admits that the site does not have the speed or capacity of YouTube.

But, as the 80 sites Hasvitz bookmarks on his computer indicate, there is no shortage of videos available. It’s just a matter of where to find and share them. Until these websites get it right, teachers will keep innovating. “Teachers are very resourceful,” says Mammano. “If there’s a piece of content they think will help students, they’ll find it.”